Equities - Narrative (Details) (USD $)	12 Months Ended				3 Months Ended	12 Months Ended
	Aug. 31, 2014	Aug. 31, 2013 pools	Aug. 31, 2012	Aug. 31, 2011	Aug. 31, 2013 Non-qualified Equity Certificates [Member]	Aug. 31, 2013 Patronage refunds	Aug. 31, 2012 Patronage refunds	Aug. 31, 2011 Patronage refunds	Aug. 31, 2012 Patronage refunds and capital stock	Aug. 31, 2011 Patronage refunds and capital stock	Aug. 31, 2010 Patronage refunds and capital stock	Aug. 31, 2013 Capital equity certificates	Aug. 31, 2012 Capital equity certificates	Aug. 31, 2011 Capital equity certificates	Aug. 31, 2013 8% Preferred Stock [Member]	Aug. 31, 2013 Class B Preferred Stock [Member]
Class of Stock [Line Items]
Net income		$ 996,328,000	$ 1,335,719,000	$ 1,061,028,000		$ 841,386,000	$ 969,862,000	$ 674,678,000
Dividends and equities payable		390,153,000	578,809,000	400,216,000		284,769,000	378,719,000	260,125,000				101,293,000	195,999,000	136,000,000
Patronage distribution		711,900,000			129,500,000				976,000,000	676,300,000	402,400,000
Cash partonage dividends payable		284,800,000
Cash patronage dividends paid		380,947,000	260,666,000	141,513,000
Patronage source earnings, percentage allocated to reserves		10.00%	100.00%
Capital equity certificates, number of pools		2
Equity redemptions, age		70 years
Retirement of equity certificates	101,300,000
Retirements of equities		(193,413,000)	(145,722,000)	(61,193,000)
Preferred stock, dividend rate, percentage		8.00%													8.00%	7.875%
Preferred stock, shares outstanding															12,272,003	11,319,175
Preferred stock, redemption amount															306,800,000	283,000,000
Preferred stock dividends paid		$ (24,544,000)	$ (24,544,000)	$ (24,544,000)